A large number of implants which are usual nowadays are inserted into the human or animal body for example with the assistance of a catheter or the like, without the surgeon being able to directly view the implantation location.
It is therefore frequently necessary for the correct position of the implant to be ascertained by other means. For that purpose, use is mostly made of imaging apparatuses which operate for example with X-rays and which enable the surgeon to judge the positioning of the implant, on the basis of the images obtained.
As many implant materials do not leave behind a sufficiently high-contrast image impression on the images obtained with the methods which are usual nowadays, in general so-called markers are applied to the implant at defined positions. The material of such markers is so selected that it affords a sufficiently high-contrast image impression, which permits conclusions to be drawn in regard to the position of the implant.
Markers of that kind generally comprise solid bodies which are impervious in regard to the radiation used for the imaging procedure. Such a solid body is inserted into the opening in the main body of the implant and connected to the main body by pressing or additionally or alternatively by welding.
Thus for example WO 97/33534 discloses a stent in which individual X-ray-opaque marker elements of gold are fitted into openings in the main body of the stent and are pressed to the latter in order to make a mechanical connection between the marker element and the main body of the stent. In that case the marker elements are in part also deformed in the manner of a rivet. Similar X-ray markers for a stent are known from U.S. Pat. No. 6,022,374. They are of an oversize in relation to the opening and are pressed into the opening, with deformation of the stent material delimiting the opening.
Both those alternative structures suffer from the disadvantage that the implant is subjected to in part really high mechanical loadings in the region of the opening, in the pressing operation. It is precisely in the case of the relatively fragile structures as are represented for example by stents that unwanted damage to the main body can rapidly occur in that region. That is particularly harmful because it cannot be immediately detected and possibly only causes failure to occur in the implanted condition. Thus for example in the case of a stent the structure may involve unwanted sharp broken edges which possibly even damage the surrounding tissue. It will be appreciated that equally the marker element may also come loose from the implant, which is undesirable.
In other known variants, the marker element is welded to the adjoining main body of the stent. That is known for example in relation to a stent from U.S. Pat. No. 5,632,771. Here, as moreover also in the case of the above-mentioned alternative configurations, there is the disadvantage that the opening and the marker element must be produced with a relatively accurate fit in order to ensure that a sufficient mechanical bond is achieved. All these variants therefore involve relatively expensive manufacture. In addition, in all known variants, the amount of freedom in terms of varying the geometry of the marker or the opening is restricted from economic points of view as different respective markers have to be produced for different openings.